The present invention relates to an automatic water inlet switching device for an oscillating sprinkler. An actuation stick of the operation unit is operable inside a bounded space so that in the water inlet switching operation the bending angle of the actuation stick is limited within the bounded space and the actuation stick will move against one of the push faces thereof so as to produce a built-up force to instantaneously spring away the movable swinging seat to pivot to one side no matter what the water pressure is high or low in operation.
In general, the common water sprinkler for garden use is equipped with a switching device for varying the direction of water flow as shown in FIG. 1 of a European patent EP0826427A2. It has a coupling unit 10 provided with a couple of water outlet ports 11 that are controllably engaged with a control unit 14 which is controlled by a spring 12 and a control stick 13 so as to make the sprinkler operated by way of the water pressure. In operation, when the control stick 13 is driven by an operation device to swing to and come into contact with one side of the stop groove of a restraint unit, the control stick 13 will be forcedly biased to the other direction, and the spring 12 under the influence of the biased control stick 13 will drive the flat board of the control unit 14 to switch to the other side to cover up the other water outlet 11 to change the direction of the flow. So, the control stick 13 must be exerted by a force with a torsion force gradually built up on the spring 12 to make the control unit 14 switched smoothly. However, if the spring 12 is not limited by a bounded space, the torsion produced by the spring 12 can not be concentrated and be dispersed easily, resulting in the torsion of the spring 12 less than the suction force at the sealed end of the control unit 14 when the water pressure is high. This will cause the outlet port 11 unable to be sealed, and the spring 12 will remain so deformed in bending in abutment against the control unit 14 for a long period of time as well. The spring 12 will suffer from fatigue as a result of that reason, making the operation life thereof shortened.